The present invention relates to a light source for a multiple image projection device.
Described in U.S. patent application Ser. No. 611,577 filed Sept. 8, 1975 which is assigned to the same assignee as this application is a "Character Display and Input Device" which typically serves as an input terminal for a computer, teletype or the like.
In parallel with the development of electric typewriters, computers, printers, ticket vending machines, inventory systems and the like has emerged the need for input devices which are adapted to enter a selected one of a tremendous number of data items into the system. A typical application to which the present invention is particularly suited is an input device for a system for transmitting both Japanese and Roman characters. Although there are only 26 Roman characters which can be easily input by a well known keyboard, the Japanese written language comprises katakana phonetic characters for writing non-Japanese words, hiragana phonetic characters for writing Japanese words and thousands kanji (Chinese) characters which are combined with the hiragana characters in writing Japanese words. In an input device for a system to transmit both Japanese and Roman characters, the number of characters which must be input into the system is generally as high as 3000 or 4000.
In the above mentioned prior patent disclosure, a large number of characters are formed on a sheet such as microfiche. The characters are further divided into classes such as a class of Roman alphabet characters, a class of Japanese hiragana characters, a class of Japanese katakana characters and a plurality of classes of Chinese characters arranged phonetically according to their leading syllables. Each class contains a predetermined number of characters. The characters are arranged in an alternating arrangement on the microfiche which is movable relative to a mask formed with apertures in such a manner that at each position of the microfiche all of the characters of a corresponding class are displayed through the respective apertures of the mask. Class selection means comprising one or more switches control drive means to move the microfiche so that the desired class of characters is displayed. Character selection means allow selection of the desired character and feed an electrical signal corresponding thereto to an electric typewriter, computer, teletype device or the like. The character selection means may comprise a light pen or switches provided to the respective apertures of the mask.
In one embodiment of said prior patent disclosure the microfiche is illuminated from behind by means of an optical fiber arrangement comprising an optical fiber for each aperture in the mask. More specifically, the optical fibers are bundled together at one end facing a light source. The other ends of the fibers face the characters on the microfiche behind the apertures in the mask. In this manner, light from the lamp is piped through the optical fibers to illuminate the respective characters from behind. Whereas this arrangement has proven to be quite effective in practical application, the manufacturing cost is rather high due to the operations required to fabricate and mount the optical fibers. This arrangement also limits the amount by which the thickness of the device can be reduced.
In another embodiment of said prior patent disclosure the optical fibers are respectively replaced by light emitting diodes. This arrangement also involves rather high manufacturing costs and limits the packing density of the characters on the microfiche.